DESCRIPTION: A long term goal of the proposed research is to elucidate the molecular mechanisms underlying morphogenesis and differentiation in the mammalian central nervous system (CNS). Homeobox-containing genes and other transcription factors, as well as a variety of signaling molecules, specifiy position in the Drosophila embryo. The mamalian homologs of some of these molecules play key roles in patterning the neural tube. Downstream targets of such regulatory genes, some of which are likely to reside on the cell surface, are thought to mediate region-specific neural interactions in the developing CNS. The study of such molecules may be directly relevant to the eventual understanding of genetic diseases that disrupt nervous system development and function. The applicant has used a novel strategy to identify regionally expressed cell surface molecules that may mediate pattern formation and axon guidance in the developing neural tube. Immunosuppression methods were used to produce monoclonal antibodies (mAbs) against antigens present in retinoic acid (RA)-treated embryonal carcinoma cells that express neuronal markers and high levels of region-specific regulatory genes. Consistent with roles for the corresponding antigens in patterning events, the mAbs - designated CARO1 through CARO5 - label the spinal cord and caudal but not rostral regions of the developing brain. Moreover, mAbs CARO2 and 5 recognize cell surface proteins that are preferentially expressed in the embryonic floor plate. These findings suggest that the CARO2 and 5 antigens are novel floor plate markers that may promote floor plate and motor neuron differentiation. In order to test this hypothesis, immunohistochemical methods will be used to determine the spatiotemporal distribution of the CARO2 and 5 epitopes in the developing rodent neural tube, cDNA cloning will be used to determine the primary structures of the CARO2 and 5 proteins, and a variety of cell culture assays will be used to determine whether the CARO 2 and 5 proteins promote floor plate or motor neuron differentiation, and possibly axon outgrowth, in vitro.